Hardware Reference
In-Depth Information
Photo 2.1
ISA/EISA and PCI expansions slots
Like the PC-XT, the standard PC/AT also provided eight expansion slots.
Six of these slots were fitted with two connectors (62- and 36-way) while two
positions (slots 1 and 7) only had 62-way connectors. Slot positions 1 and 7
were designed to accept earlier 8-bit expansion cards which made use of the
maximum allowable height throughout their length. If a 36-way connector
had
been fitted to the system motherboard, this would have fouled the lower edge
of the card, preventing effective insertion of the card!
Finally, it should be noted that boards designed for AT systems (i.e. those
specifically designed to take advantage of the availability of the full 16-bit
data bus) will usually offer a considerable speed advantage over those which
were based upon the 8-bit PC expansion bus. In some applications, this speed
advantage was critical.
PC expansion cards
Expansion cards for PC systems tend to vary slightly in their outline and dimen-
sions (see Figure 2.2). However, the
maximum
allowable dimensions for the
adapter and expansion cards fitted to PC (and PS/2) equipment is usually quoted
as follows:
Height
Length
Width
Standard
System type
in.
mm
in.
mm
in.
mm
ISA
8-bit PC and PC-XT
4.2
107
13.3
335
0.5
12.7
EISA
16-bit PC/AT
4.8
122
13.2
335
0.5
12.7
MCA
PS/2
3.8
96
13.2
335
0.5
12.7
PCI
PC/AT
4.8
122
7.3
185
0.5
12.7
With the exception of slot 8 in the PC-XT, the position in which an adapter or
expansion card is placed
should
be unimportant. In most cases, this does hold
